The invention relates to optical particle size apparatus and has particular application to apparatus known as small volume particle size analysis apparatus. Those skilled in the art will recognize that particle size analyses is generally categorized by the collective volume of the mixing tank and circulator apparatus. So called small volume particle size analysis apparatus commonly has a mixing tank and circulator total volume of approximately 300 milliliters. Ultra-small systems are also known which are much smaller as well as larger systems having a combined volume of approximately four liters. Such apparatus has application in many process industries. Examples include process control for the cement, cosmetics and pharmaceutical industries.
The general nature of the present apparatus will be better understood by reference to U.S. Pat. No. 4,496,244 which issued on Jan. 29, 1985 to Albert R. Ludwig and which is assigned to the same assignee as the present application.
In using such apparatus it is common to prepare a slurry by suspending the particles in a liquid and to continually stir the slurry to provide a homogeneous suspension. The slurry is then continually recirculated through the analyzer during analysis.
Typical apparatus of this type utilizes a mixing chamber in which a stirring impeller is disposed to thoroughly mix the particles. The slurry with its suspended particles is pumped from the reservoir or mixing tank to the analyzer and then returned to the reservoir. The apparatus conventionally includes a sample cell. Thus, It is well known that a mixing tank can be utilized with a stirring impeller inserted in the tank to mix the slurry. However, as the mixture is circulated by a pumping action from the tank to an analyzer celt, non-uniformity of distribution and particle settling can occur.
It is of vital importance that the distribution of the particles in the slurry in the sample cell be representative of the entire statistical population. This is obviously necessary to ensure valid data collection for analysis.
A problem in such apparatus is that as the slurry is circulated by a pumping action from the mixing tank to the sample cell there may be a non-uniform distribution of particles in the sample cell.
The prior art has used an ultrasonic probe to provide particle deagglomeration in the mixing tank or before the slurry enters the recirculation apparatus. While this arrangement does produce better particle deagglomeration than apparatus that does not incorporate such ultrasonic probes, the arrangement is still not wholly satisfactory. More particularly it is not satisfactory to apply energy to the entire volume of the reservoir because the energy added to individual particles is not uniform and excessive heat is added to local ares of the slurry.